Circuit interrupter



1943- B. P. BAKER ETAL CIRCUIT INTERRUPTER Filed April :5. 1945 INVENTORS I Pia/? (2'14:

WITNES ES:

jar/21m? TORNEA" Patented Nov. 16, 1948 CIRCUIT INTERRUPTER Benjamin P. Baker, Turtle Creek, and Donald C.

Harker, Wilkinsburg, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 3, 1945, Serial No. 586,400

7 Claims.

This invention relates to circuit interrupters and, more particularly, to circuit interrupters in which the arc is extinguished by a blast of air or gas directed to blow the arc across arc splitters or other devices for extinguishing the arc.

Recently we have encountered a phenomenon not met with in low and moderate capacity circuit interrupters. In high capacity circuit interrupters and, particularly, for interrupting low frequency currents, the heat of the are acting upon the are splitters tends to generate a large volume of gases. The volume of gas often is so great, and is generated so rapidly that a considerable back pressure is developed. In some cases, it has been found that the back pressure exceeds the pressure of the air or other gas employed to force the arc against the splitters. Under these conditions, a hot blast of gas carrying metal vapor and carbonaceous products may surge back past the contacts and deposit a metallic glaze on the surrounding insulation as well as carbonizing or charring the adjacent organic insulating materials. This phenomenon is designated as gas blow-back. Because of this phenomenon, the insulation adjacent to the contacts of the are interrupter is rendered progressively more conducting as the number of circuit interruptions increases. Failure of the interrupter to perform its function soon occurs because the arc current flows through the layer of conducting metal and carbon deposited on the insulation as well as through the carbonaceous surface of the organic insulating material deteriorated by the hot gases impinging thereon. I

The object of this invention is to increase circuit-breaker interrupting capacity by providing means capable of maintaining adequate insulation under adverse gas blow-back conditions.

Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description and drawing, in which:

Figure l is a fragmentary View, partially in cross-section, of a circuit interrupter according to prior artconstruction,

operation due to gas blow-back. In the circuit interrupter In a stationary contact member l2 and a movable contact member 14 produce an arc when separated under load. The movable contact i4 is disposed for movement within the slot 18 in the insulating spacers l6. Insulating cover members 20 (only the one covermember being shown in the drawing) are applied to the spacers l6 thereby providing a chamber for confining and guiding the are and the compressed air or gas blast. An insulating base 2|, dis-posed in contact with the ends of the spacers I6, is p o with a bore 22 having an enlarged threaded portion 24 for engaging the compressed air or gas blast tube 26. The blast tube 26 is connected to a suitable source of compressed air or gas. When contact members 12 and M are separated during a circuit interrupting operation an arc will be formed between them; and compressed air or other gas is conveyed through the blast tube 26 to the bore 22 and is directed against'the arc to blow the are against arc splitters 28 forming an arc confining and extinguishing means. The are splitters 28 are usually composed of organic material capable of giving off an arc extinguishing gas when subjected to an arc. Chemically treated cellulose sheet material known as fiber 0r hor'n fiber has proven to be an excellent are splitter material.

The insulating spacers IS, the cover members 20, the insulating base members 2| and the blast tube 25 are generally composed of organic materials. Fiber makes satisfactory spacers. Laminated phenol-aldehyde, melamine-aldehyde or urea-aldehyde resinous materials are commonly used for making the cover members 20, base members 2| and blast tubes26.

When the are is blown against the arc splitters 28 by a blast of air or gas from the tube 25, the intense heat of the arc causes a gas to be evolved therefrom. The arc also heats up the gas blast itself and under certain high current interrupting conditions the hot expanded volume of gases cannot escape through the arc splitters as fast as it expands so that it develops a pressure high enough to reverse the air or gas flow and is sufiicient to blow back against the spacers l6,'the base member 2| and cover members 20. While this condition occurs at various frequencies at high current short circuits, it is especially prominent when. currents of low frequencies, such as 25 cycle currents are being interrupted since the time of arc duration is greater before zero current is reached. With low frequency currents the time of exposure of the insulation to the hot gases is longer. The heated gases carry metal vapor volatilized from the faces of the contact members by the arc. Likewise carbon particles may be present as a result of the action of the arc on the material forming the arc splitters. The metal vapor and carbon is deposited by the gas blowback upon the cooler insulation, particularly upon the basemember 2i bore 22 and in some cases inside the blast tube 25. The composition and constructions heretofore employed for the base member and the blast tube is such that the metal vapors and carbon adhere firmly thereto. Further the hot gases carbonize the organic insulation forming these members. Since the maximum voltage gradient is present at the area adjacent the bore 22. the presence of such conducting deposits is highly undesirable. In practice it has been found that the deposit of metal and carbon increases with each gas b1ow-baclr and after a few circuit interrupting operations giving rise to gas blow-back enough metal and carbon is deposited on the insulation to short circuit the arc and prevent successful arc extinction and circuit interruption.

The phenomenon of gas blow-back therefore limits the maximum short circuit that a given circuit interrupter may be subjected to. In many cases a circuit interrupter would be capable of handling and interrupting much higher currents but for the adverse effects of gas blow-back.

It has been discovered that the adverse effects of gas blow-back occurring when heavy currents are interrupted in a compressed-air circuit breaker of the cross-blast splitter type, may be eliminated by employing a novel insulating structure, in and around the contacts, composed of an inorganic insulating material that will not metal vapor glaze or pick up metal and carbon coat- We have found that an insulating ring 32 meetings when subjected to hot gases carrying metallic vapor and carbon. It has been discovered, in particular, that the insulation'at the throat, or outlet end, of the air or gas blast tube, where the voltage gradient over the surface of the insulation is greatest, should be prepared from a nonvapor-glazing, high thermal shock resisting, ce-

ramic insulating material.

For an illustration of the application of this invention, reference should be had to Figure 2 of the drawing showing a portion of a circuit interrupter, having a stationary contact l2 and a cooperating movable contact i l, the latter passing through the slot if? in the insulating spacer iii. The are splitters 28 are commonly composed of a material capable of giving off an arc-extinguishing gas. Many arc-extinguishing gasevolving resinous substances including horn fiber have been employed for the arc splitters. In some cases phenolic resins, melamine aldehyde resins, urea resin, polystyrene, ethyl cellulose, and the like, with or without additions of arc-extinguishing substances such as boric acid, have been made use of for makin arc splitters. The resins have been molded with reinforcing materials therein such as asbestos or glass cloth. The insulating base member 3t: to which the contact member 62 and the other structural members are joined is fitted with a blast tube 26 for conveying air or other gases for blowing the are developed upon separation of the contacts 02 and it into the arc splitters l8.

The adverse effect of the gas blow-back may be substantially eliminated by introducing a ring 32 composed of a non-vapor-glazing, thermal shock resisting, insulating ceramic material. The ring 32 forms an extension of the blast tube 26.

ing the above requirements may be prepared from zircon porcelain. Zircon porcelain is not metallized significantly by the metal vapors in blow-back gases. Due to the heat shock when the intensely hot blow-back gases impinge on the ring, it is necessary that the insulation have an exceptionally high thermal shock-resistance. and this quality is possessed by zircon porcelain in a measure superior to other ordinary electrical porcelains. The zircon porcelains have excellent overall electrical insulating and mechanical strength characteristics. Furthermore, zircon porcelains are dense and will not absorb moisture, thereby maintaining their predetermined electrical insulating characteristics in spite of adverse weather conditions. A typical zircon porcelain suitable for the application was prepared from the following ingredients.

sintered alumina can be employed as the ceramic material for the ring 2 3 with similar satisfactory results since it is non-vapor-glazing and non-moisture absorbing and has good thermal shock-resistance. It possesses electrical insulating properties of a high order. Furthermore, we have found that porcelains containing less than 65% silica are suitable for use in the present application since porcelains of this composition will not acquire an adherent film of metal from the vaporized metal present in the blow-back gases. Examples of suitable materials are kyanite and sillimanite.

Ordinary high-silica electrical porcelain is not satisfactory since it will crack readily on being subjected to the heat of the blow-back gases. Also the porcelain having over 65% silica will pick up metal in the form of a metal glaze from the gases and form conducting surface films.

It will be understood that the entire blast tube 2% may be composed from the non-vapor glazing ceramics such as zircon porcelain. This is necessary if the end of the blast tube extends into the arc chamber.

In order to assure the best results in highcapacity air-blast circuit interrupters, it has been found that the entire insulation adjacent the contacts and subject to high voltage gradients, which may be subjected to the hot blowback gases, should be composed of the non-vapor glazing insulating ceramics. A suitable insulating member 48 for this purpose is illustrated in Fig. 3. The insulating member 40 is composed of a cylindrical portion 52 forming an extension of the blast tube 25. A laterally expanding portion 44 providing for expansion of the air or gas blast in the direction of the arc splitters is formed with recesses or slots 46 and 48 to accommodate the moving contact and the stationary contact members it and 52, respectively. Grooves 52 may be provided in the upper edge of the member 40 for maintaining the tips of the splitters 28 in position. The member 40 may be composed of zircon porcelain or sintered alumina or other refractory containing less than silica as described previously. The walls of such ceramic materials will not carbonizeor char, or become electrically conducting by the action of gas or are heat. Any carbon or metal vapors in the gases generated or developed during an arcextinguishing operation and driven thereagainst by gas blow-back will not be deposited and retained on the walls of the insulator member 49. Therefore, the contacts will be satisfactorily insulated for the life of the circuit breaker in spite of heavy duty operation giving rise to gas blowback.

Circuit interrupters of Figures 2 and 3 composed of the herein described non-vapor glazing thermal shock resisting ceramic materials may be efiectively employed to interrupt circuits of higher current strength at lower frequencies than the same size conventional circuit interrupters lacking this insulating structure disposed at the critical areas subject to gas blow-back adjacent the contacts.

While gas blow-back is particularly pronounced with are splitters composed of organic gas evolving materials, in some cases the heat of the are alone may cause such a large expansion effect that a hot gas blow-back may occur even if the arc splitters are composed of inorganic materials.

Since certain changes in carrying out the above processes and certain modifications in the compositions which embody the invention may be made without departing from its scope, it is intended that all the matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. An electric circuit interrupter comprising, in combination, conductor means between which an arc is formed on interruption of the circuit, are extinguishing and confining means disposed along the path of the are from which an arc extinguishing medium can be evolved due to the heat of the are for extinguishing the same, and a blast tube for conveying and directing a gaseous medium for blowing the are into the arc-extinguishing and confining means, at least that portion of the blast tube nearest the conductor means being composed of an insulating, nonmoisture absorbing, non-vapor glazing, thermal shock-resisting porcelain type ceramic having less than 65% silica.

2. An electric circuit interrupter comprising, in combination, conductor means between which an arc is formed on interruption or the circuit, arc extinguishing and confining means disposed along the path of the are from which an arcextinguishing medium can be evolved due to the heat of the are for extinguishing the same, and a blast tube for conveying and directing a gaseous medium for blowing the arc into the arc-extinguishing and confining means, the portions of the circuit breaker structure adjacent to the conductor means, other than the arc confinin and extinguishing means, being composed of an insulating, non-moisture absorbing, non-vapor glazing, thermal shock-resisting porcelain type ceramic having less than 65% silica.

3. An electric circuit interrupter comprising. in combination, conductor means between which an arc is formed on interruption of the circuit. are extinguishing and confining means disposed along the path of the are from which an arc extinguishing medium can be evolved due to the heat of the are for extinguishing the same, and a blast tube for conveying and directing a gaseous medium for blowing the are into the arc extincombination,

embodying the structures l lain having less than 65% guishing and confining means,- at least that portion of the blast tube nearest the conductor means being composed of zircon porcelain having less than silica.

4. An electric circuit interrupter comprising, in conductor means between which an arc is formed on interruption-of the circuit, arc extinguishing and confining means disposed along the path of the are from which an are extinguishing medium can be evolved due to the heat of the are for extinguishing the same, and

a blast tube for conveying and directing a gaseous medium for blowing the arc into the arc extinguishing and confining means, at least that portion of the blast tube nearest the conductor means being composed of sintered alumina.

5. An electric circuit interrupter comprising, in combination, conductor means between which an arc is formed on interruption of the circuit, arc extinguishing and confining means disposed along the path of the are from which an arc extinguishing medium can be evolved due to the heat of the are for extinguishing the same, and a blast tube for conveying and directing a gaseous medium for blowing the arc into the arc extinguishing and confining means, the portions of the circuit breaker structure adjacent to and surrounding the conductor means, other than the arc confining and extinguishing means, being composed of zircon porcelain having less than 65% silica.

6. An electric circuit interrupter comprising, in combination, conductor means between which an arc is formed on interruption of the circuit, arc extinguishing and confining means disposed along the path of the arc, and a blast tube for conveying and directing a gaseous medium for blowing the arc into the arc extinguishing and confining means, the portions of the circuit breaker structure adjacent to and surrounding the conductor means, other than the arc confining and extinguishing means, being composed of zircon. porcesilica.

7. An electric circuit interrupter comprising, in combination, conductor means between which an arc is formed on interruption of the circuit, are extinguishing and confining means disposed along the path or the are from which an arc extinguishing medium can be evolved due to the heat of the are for extinguishing the same, and a blast tube for conveying and directing a gaseous medium for blowing the are into the arc extinguishing and confining means, the portions of the circuit breaker structure adjacent to and surrounding the conductor means, other than the arc'confining and extinguishing means, being composed of sintered alumina.

BENJAMIN P. BAKER. DONALD C. HARKER.

REFERENCES CITED The following references are of record in the file of this patent:

' UNITED STATES PATENTS Number Name Date 1,682,251 Riddle Aug. 28, 1928 1,696,614 Steele Dec. 25, 1925 2,240,654 Jochem et al. May 6, 1941 2,272,338 Fessler Feb. 10, 1942 2,272,380 Ludwig et al Feb. 10, 1942 2,276,859 Nau Mar, 17, 1942 2,310,728 Bartlett 'Feb. 9, 1943 

